A head-up display (HUD) is a transparent or see-through electronic display that presents visual information to a viewer without requiring the viewer to look away from his current viewpoint. The term HUD stems from a user, such as an aircraft pilot, being able to view information with his head positioned “up” and looking forward, instead of angled down looking at a lower instrumentation panel. HUDs can have a fixed display element, such as mounted to the cockpit of an aircraft. HUDs can also feature a display element that moves in conjunction with the position and orientation of the head of the user. HUDs with movable displays are also known as head-mounted displays or helmet mounted displays (HMDs)
A typical HUD contains three primary components: a projector unit, a combiner, and a video generation computer. The projection unit in a HUD is an optical collimator setup: a convex lens or concave mirror with a cathode ray tube, light emitting diode, or liquid crystal display at its focus. The combiner is typically an angled flat piece of glass located directly in front of the viewer. This flat piece of glass acts as a beam splitter and redirects the projected image to allow the viewer to see the background scene in his field of view simultaneously with the projected image. The computer interfaces with the projection unit of the HUD, and generates the imagery and symbology to be displayed by the projection unit. Typical aircraft HUDs display symbols or indicators representing flight data, such as: airspeed, altitude, a horizon line, heading, turn, bank, slip and skid parameters. In addition to real-time flight information, other types of symbols and data may also be presented on aircraft HUDs. For example, military applications include symbols representing weapon systems and sensor data, such as: target designation, closing velocity, range, launch acceptability, line of sight, and weapon status.
Often the color (or color-related properties) of the background environmental features visible through the HUD may conflict or interfere with the symbol to be displayed on the HUD superimposed onto the background view. For example, the particular color or other chromatic properties (e.g., hue, brightness, saturation) of the background region in combination with the particular color or other chromatic properties of the symbol, may cause problems or difficulties for the viewer to properly perceive the symbol relative to the background. In particular, the color combination may be such that it would be difficult to distinguish the symbol from the background, or that would result in a different color actually being perceived by the viewer different from the originally intended color of the symbol. In certain situations, the displayed symbology may be time-sensitive or otherwise of crucial importance to the viewer (e.g., an indication of real-time flight information), where adverse consequences may result if the displayed information is incorrectly perceived or improperly comprehended by the viewer.
U.S. Pat. No. 6,809,741 to Bates et al, entitled: “Automatic color contrast adjuster”, discloses a color contrast adjuster that automatically selects and applies a new color combination for text and background based on the current color combination, if the current color combination is a problem color combination. The text can be any text object and the background can be any background object whose color can be determined. The color contrast adjuster can store multiple problem and preferred color combinations for each user, and can replace a problem color combination with a preferred color combination. The color contrast adjuster can provide example color combinations to a user, allow the user to select a better color combination, and add the preferred and problem combination to user preferences.
U.S. Pat. No. 7,184,063 to Shum et al, entitled: “Adaptive color schemes”, discloses techniques for adaptive changing a displayed foreground color when a conflict between the displayed foreground color and an extracted background color is detected. Upon detection of such a conflict, a new foreground color is selected in accordance with a predetermined legibility condition. A color pool candidate may be considered to be a viable foreground color if a legibility value for the candidate color in relation to the extracted background color exceeds a predetermined legibility threshold value.
U.S. Patent Application No. 2012/0092369 to Kim et al, entitled: “Display apparatus and display method for improving visibility of augmented reality object”, discloses improving the visibility of each augmented reality object by displaying each object differently from the background. The display apparatus and display method may improve the visibility by outputting a list of overlapped objects or a map of overlapped objects, or by enlarging a complex area in which objects are densely disposed, to reduce overlapping of the objects.
U.S. Patent Application No. 2012/0127198 to Gundavarapu, entitled: “Selection of foreground characteristics based on background”, discloses a text colorization system that automatically sets the foreground text color based on one or more background colors over which the text is displayed. A text colorization system identifies a background color neighboring each pixel of a string of text. For each pixel region, the system selects a color to satisfy one or more colorization criteria. The system sets the text color at each region based on the selected color. The system then displays the layered image to the user, such as through a computer display or mobile device display.
U.S. Patent Application No. 2013/0147826 to Lamb, entitled: “Display of shadows via see-through display”, discloses a method of operating a display device with a see-through screen. An image of an object is displayed on the display screen, while displaying an image of a shadow cast by the object onto the background scene. A location of the shadow is determined in an image of the background scene. An enhanced image of the background scene is rendered by increasing a relative brightness in a region adjacent to the shadow compared to the brightness within the shadow, and the enhanced image is displayed.
U.S. Patent Application No. 2013/0222424 to Morinaga et al, entitled: “Object display device and object display method”, discloses a display device with a pattern extraction unit that extracts a region where an object is easily visually recognized when the object is overlaid and displayed in an image in real space, from the image in real space, based on information about the size and color of the object and about the color of the image in real space, acquired by an image analysis unit. A display position correction unit corrects the display position of the object to the region, to facilitate visual recognition of the object and enhance various effects, such as informativeness.
U.S. Patent Application No. 2013/0265232 to Yun et al, entitled: “Transparent display apparatus and method thereof”, discloses a method and apparatus for displaying information on a transparent display such that the user can better discern the displayed elements in view of objects seen behind the transparent display. At least one sensor senses a position of an object and a position of a user. An area of the display through which the object is viewable by the user is determined, based on the positions of the object and of the user, and the information is displayed on the transparent display based on the determined area.
U.S. Patent Application No. 2007/0013495 to Suzuki et al, entitled: “Vehicle drive assist system”, discloses a system for displaying lane markers indicating a travelling lane of the driver's vehicle, in a manner that allows better recognition of the lane markers under unfavorable environmental conditions. The system controller obtains lane information from various sources, such as an image of the road surface captured by a camera, temperature sensed by a thermistor, and snow conditions based on the sensed temperature and the slip rate indicated by an ABS unit. A sight line sensing system detects a view point position of the driver. An image of two lane guides, corresponding to opposite side edges of the travelling vehicle viewed from the view point of the driver through the vehicle front glass, is generated based on the detected view point position and obtained lane information. A display unit displays the image on or through the vehicle front glass. The background color at the lane guides (road surface) is detected, and the display color of the lane guides is set so as to increase the contrast relative to the detected background color.
U.S. Patent Application No. 2014/0253579 to Babaguchi, entitled: “Headup display, display method for headup display, and program for headup display”, discloses a headup display (HUD) intended to improve visual recognizability while reflecting an original display color. Prescribed information initialized to a first display color is projected on a display board arranged in a user's gaze direction. A background color visually recognized by the user through the display board is detected. A first display color is adjusted based on the detected background color, and the prescribed information is displayed in the adjusted color. In particular, the first display color is adjusted to a second display color to correspond to the difference between the detected background color and the first display color, where the difference may represent the gradation difference or based on other color information. For example, the second display color may be obtained by mixing the first display color with the complementary color most easily visually recognizable with respect to the background color, where the mixing may be based on a calculated mixing ratio.